Fe2+-Sensing α-Synuclein Iron-Responsive Messenger RNA/eIF4F Complex Binding and Regulating mRNA Translation Activation and Repression

TL;DR

This paper explores how iron influences the regulation of alpha-synuclein protein synthesis in Parkinson's disease.

Contribution

The study reveals a novel mechanism by which Fe2+ enhances α-Syn mRNA translation via eIF4F binding.

Findings

Fe2+ increases the binding affinity of α-Syn IRE with eIF4F by three-fold.

Thermodynamic analysis shows Fe2+ stabilizes the α-Syn IRE/eIF4F complex through hydrogen bonding.

Fe2+ reverses IRP1 repression of α-Syn translation by promoting eIF4F binding.

Abstract

Alpha-synuclein (α-Syn) protein plays a crucial role in the pathophysiology of Parkinson’s disease (PD). In the 5′-untranslated regions (5′-UTRs) of α-Syn, mRNA has a structured iron-responsive element (IRE) with a stem loop that regulates translation. Iron (labile as Fe2+) enhances protein synthesis rates through an IRE mRNA. This investigation aimed to describe the way in which α-Syn IRE interacts with eIF4F and establish a relationship between binding affinity and translation efficiency. The strong binding affinity of α-Syn IRE with eIF4F was demonstrated by a fluorescence-based experiment, with Ka = 8.4 × 106 M−1 at 25 °C. Fe2+ further increased (~three-fold) the affinity of α-Syn IRE with eIF4F, outcompeting binding with IRP1. With an increase in temperature (10–30 °C), Kd values increased from 35.8 ± 1.6 nM to 158 ± 8.7 nM for the interaction of α-Syn IRE with eIF4F; however, adding Fe2+ demonstrated significantly increased affinity throughout the same temperature range. Thermodynamic analyses demonstrated that α-Syn IRE/eIF4F binding occurred spontaneously, with the presence of van der Waals and hydrogen bonding. Fe2+ enhanced the α-Syn IRE/eIF4F complex’s change in enthalpic and binding free energy contributions, which led to a more stable complex formation through the involvement of more hydrogen bonding. Exogenous addition of eIF4F in depleted WG or RR lysates restored α-Syn protein synthesis. Fe2+ further boosted α-Syn mRNA translation. IRP1 repressed α-Syn translation, although the addition of Fe2+ reversed this effect by boosting activator eIF4F binding and decreasing repressor IRP1 binding. These findings reveal the significance of iron in the α-synuclein mRNA regulatory process and validate its contribution as a strong enhancer of α-Syn mRNA translation.

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